Re: [Xen-devel] [PATCH v1 4/6] vvmx: add hvm_max_vmx_msr_policy

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 06.07.17 at 12:23, <sergey.dyasli@xxxxxxxxxx> wrote:
> On Tue, 2017-07-04 at 09:04 -0600, Jan Beulich wrote:
>> > > > On 26.06.17 at 12:44, <sergey.dyasli@xxxxxxxxxx> wrote:
>> > 
>> > +{
>> > +    struct vmx_msr_policy *p = &hvm_max_vmx_msr_policy;
>> > +    uint64_t data, *msr;
>> > +    u32 default1_bits;
>> > +
>> > +    *p = raw_vmx_msr_policy;
>> > +
>> > +    /* XXX: vmcs_revision_id for nested virt */
>> 
>> There was no such comment (presumably indicating something that
>> yet needs doing) in the old code - what's this about? Can't this be
>> implemented instead of such a comment be added?
> 
> Currently L1 sees vmcs_revision_id value from the H/W MSR. Which is
> fine until live migration is concerned. The question is: what should
> happen if L1 is migrated to some other H/W with different vmcs id?
> One possible solution is to use "virtual vmcs id" in the policy object.

Are there any other (reasonable) ones, besides forbidding
migration (live or not). Otoh, if migration between hosts with
different IDs is allowed, won't we risk the page layout (which
is intentionally unknown to us) changing as well? Or in order
to be migrateable, such guests would have to be forced to
not use shadow VMCS, and we'd have to pin down (as part of
the guest ABI) the software layout we use.

Jan


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